K/GaAs(110) interface: Initial stages of growth and the semiconductor-to-metal transition

The K/GaAs(110) interface has been studied to explore the initial stages of formation of a model metal-semiconductor interface. For K deposition at room temperature, thermal-desorption spectroscopy measurements showed that the K overlayer saturates at a coverage that we define as ${\mathrm{\theta }}_{\mathrm{sat}}$. K adsorption results in a work-function decrease of ∼2.9 eV by ∼0.4 ${\mathrm{\theta }}_{\mathrm{sat}}$ with no distinct minimum being observed up to ${\mathrm{\theta }}_{\mathrm{sat}}$. Electron-energy-loss measurements of the developing interface at room temperature revealed a continuous narrowing of the interfacial band gap for increasing K coverages, being reduced to ∼200 meV at ${\mathrm{\theta }}_{\mathrm{sat}}$. Finite excitation intensity within the band gap at room temperature was quenched at low temperatures, suggesting the existence of a true interfacial band gap at coverages ≤${\mathrm{\theta }}_{\mathrm{sat}}$. At a coverage of ∼1.2 ${\mathrm{\theta }}_{\mathrm{sat}}$, obtained by low-temperature (∼135 K) deposition onto a room-temperature saturated layer, the semiconductor-to-metal transition was observed. In contrast, rapid metallization of the interface was observed upon low-temperature deposition of K onto clean GaAs(110), indicating a distinctly different growth mode.